The King's Face(왕의 얼굴)

Though Crown Prince Gwanghae (Seo In Gook) is the son of a concubine and has always had the question of birthright looming over his head, he is eventually deemed the approved successor to the throne. But shortly after his father's passing, the royal edict is destroyed, giving the Northern faction the opportunity to contest his rule. Without any piece of evidence that can confirm his legitimacy, Prince Gwanghae must rely on the only thing that connects him to the royal bloodline: his own face.

If you like The King's Face check out the movie
The Face Reader
which this drama is loosely based upon.